One incident that I do know of is the loss of two RAF chinooks in one day. Both were on first test flights after maintenance, one in England and one in the Falklands. As the aircraft lifted it to the hover there was a bang and the front rotors slowed down and mingled with the rear rotors. It turned out that the techs had put the drive shaft to the front gerabox in backwards on both machines. both were written off but no lives were lost
